In the field of annealing various semiconductor materials, such as ion-implanted silicon and gallium arsenide wafers for the purpose of electrically activating these wafers, it is known that the annealed semiconductor crystals will, upon heating beyond certain elevated temperatures, dissociate and decompose unless they are maintained in a carefully controlled environment. Thus, several processes have evolved for the purpose of either impeding or altogether preventing the escape of elemental gases from the surface of the semiconductor crystal being annealed at a prescribed elevated temperature, typically in excess of 800.degree. C.
Known methods for preventing such dissociation and decomposition of semiconductor crystals subjected to these elevated anneal temperatures include:
(1) CONTROLLING THE VAPOR PRESSURE SURROUNDING THE SEMICONDUCTOR CRYSTAL DURING ANNEALING IN ORDER TO CREATE AN EQUILIBRIATING ENVIRONMENT AT THE CRYSTAL'S SURFACE, AND
(2) ENCAPSULATING THE SEMICONDUCTOR CRYSTAL IN A SELECTED SOLID OR POWDER (POWDERED SOLID) IN ORDER TO CREATE AN INTERFACE BARRIER AT THE CRYSTAL'S SURFACE WHICH ALSO SERVES TO IMPEDE THE FLOW OF ELEMENTAL VAPORS AWAY FROM THE SEMICONDUCTOR CRYSTAL. Some solid encapsulants which have been used for this purpose include SiO.sub.2, Si.sub.3 N.sub.4, Al and other amorphous dielectrics.
The first of the above two prior approaches often requires critical pressure control of the environment surrounding the crystal and the vapor pressures therein in order to maintain a controlled equilibriating condition at the crystal surface. Additionally, when equilibrating gas streams are passed over a plurality of semiconductor wafers being annealed, this generally requires elaborate gas flow equipment and careful control over both the reactant materials of the gas flow process and the differential temperatures required thereby.
An example of this first approach is disclosed by R. M. Malbon et al. in an article entitled, "Annealing of Ion Implanted GaAs In a Controlled Atmosphere", Journal of the Electrochemical Society: Solid-State Science & Technology, Sept. 1976 at pages 1413-1415.
On the other hand, the second of the above two prior approaches creates obvious cleaning and contamination problems as a result of the direct physical contact between the semiconductor crystal and the surrounding solid or powdered encapsulating material. An example of this second approach is described by A. A. Immorlica et al. in an article entitled, "Capless Annealing of Ion Implanted GaAs", Applied Physics Letters, Vol. 29, No. 2, July 15, 1976 at pages 94-95.